1. Field of the Invention:
The present invention relates to a wire bonding apparatus used for fabricating a semiconductor integrated circuit (hereinafter referred to as an "IC") device.
2. Description of the Related Art:
Wire bonding apparatus is used for manufacturing an IC device in a final stage of the fabrication thereof. A conventional wire bonding apparatus will be described below with reference to drawings.
FIGS. 1 and 2 show plan views each illustrating a general configuration of an IC chip and a lead frame before or after bonding operation is performed thereto. FIG. 3 shows a cross-sectional view along line A--A' of FIG. 2, while FIG. 4 shows a plan view of a lead frame in which a plurality of IC chips are fabricated.
In FIGS. 1 through 3, the IC chip 6 has been fixed, prior to a bonding operation onto the lead frame 11, in a region surrounded by inner leads 5 for connection of the electrode pads 7 of the IC chip 6 with the inner leads 5 of an IC package by wires 20. As shown in FIG. 4, a plurality of IC chips 6 are successively arranged on a single lead frame 11 at a constant pitch for a mass production. Position marks 21a and 21b both serving as reference coordinates for the positions of all of the inner leads 5 are provided for corresponding one of the IC chip 6. Tips of some of the inner leads 5 may be used as a substitute for the position marks 21a and 21b. The IC chip 6 also has position marks 7a and 7b each constituted by an electrode pad as shown in FIG. 1.
In a conventional wire bonding apparatus for bonding the electrode pads 7 of the IC chips 6 with the inner leads 5 of the lead frame 11 as described above, a detection camera for detecting position of each of wire bond objects including electrode pads 7 and corresponding inner leads 5 is generally fixed to an XY-table moving in a horizontal direction, on which a bonding head is mounted. Before a bonding operation is carried out, the detection camera is successively moved by the XY-table to a location right above each of the position marks 7a, 7b, 21a and 21b and the bonding point of each of the inner leads 5 so as to store the coordinates of each of the electrode pads 7 and the inner leads 5. Thereafter, a wire bonding operation is carried out while moving the bonding head by the XY-table based on the stored coordinates.
FIG. 5 shows a detail of a portion of an area encompassing wire bond objects including the inner leads 5 and the electrode pads 7 of FIG. 1. In the region as shown by FIGS. 1 and 5, a detection camera is first moved to each of the positions of specific electrode pads 7a and 7b serving as reference coordinates of the IC chip 6. Subsequently, the detection camera is moved to a bonding point 28b of an endmost inner lead 5b to detect the coordinates of the bonding point 28b of the specific inner lead 5b. The detection camera is then moved to a next bonding point 28c of another inner lead 5c adjacent to the inner lead 5b to detect the coordinates of the bonding point 28c of the adjacent inner lead 5c. In a similar manner, the detection camera is successively moved to detection points 28 of other inner leads 5 to detect their coordinates.
In a conventional wire bonding apparatus as described above, the detection of the position or coordinates of the bonding point of the electrode pads and each of the inner leads by using the detection camera cannot be carried out simultaneously with a bonding operation for the electrode pads and the inner lead. In a recent IC package, lead frames, ceramic packages, tape carriers are employed in which a large number of pins are involved, hence the allowable deviation of each inner lead from a design position thereof is very small because of the small dimension of the inner lead. Consequently, detecting the coordinates of each of the bonding points of a large number of inner leads consumes a significant amount of time, resulting in a decrease of the efficiency of wire bonding.
For example, the amount of time required for detecting the bonding point of each inner lead is about 0.08 second, so that it takes a total amount of about 24 seconds to detect coordinates for all of the inner leads of each IC chip in the case where the IC chip has as many as 300 pins. The total amount of time of 24 seconds consumed for detecting the inner lead of each IC is significant in the field of the wire bonding apparatus affecting the productivity of IC device.
In a wire bonding apparatus disclosed in JP-A-3(1991)-48434, which is shown in FIG. 6 as a cross-sectional view thereof, two detection cameras 10c and 10d are mounted on an XY-table 2b onto which a bonding head 4 holding a bonding tool 3 is mounted. The first camera 10c is used for detecting the bonding point of each of inner leads at a region above a one-pitch upstream station 12 located one-pitch upstream from a bonding station 13, while the second camera 10d is used for detecting the positions of electrode pads at a whole at a region above the bonding station. The first camera 10c for the inner leads is mounted for horizontal movement relative to the XY-table 2b so that the distance in a horizontal direction between the first camera 10c and the bonding tool 3 can be adjusted, while the second camera 10d for electrode pads is fixed to the XY-table 2b. In FIG. 6, 1 denotes a machine base, 9c denotes an optical system for the detection cameras 10c and 10d, 14 denotes an image processing unit, 16 denotes a control unit, 17 denotes an ITV monitor, 18 denotes supporting members, and 25 denotes image signals.
Simultaneously with a bonding operation of an IC chip by the bonding tool 3, the bonding points of each of inner leads of a succeeding IC chip are detected by the first camera 10c. Hence, the position detecting operation for the inner leads and the wire bonding operation are overlapped with each other in adjacent two IC chips. This increases the efficiency of the bonding operation, thereby improving the productivity of the IC device.